The present invention relates generally to antenna systems, and more particularly to a dual-band patch antenna element for circular polarization radiation.
A patch antenna is typically used to provide a quasi-hemispherical radiation pattern and linearly or circularly polarized waveforms that are necessary for satellite communications systems. However, the bandwidth of these antennas is small. Therefore, certain applications that have relatively large separation between transmit and receive frequency bands typically exceed the bandwidth provided by a conventional patch antenna. A conventional patch antenna cannot cover more than a 5% bandwidth due to its inherent narrow bandwidth characteristics.
Additionally, the bandwidth of a patch antenna may also be limited by power transfer considerations. Often the power transfer between the transmit and receive bands has losses due to reflections, which are a result of imperfect impedance matching. This reflected power loss impairs the operation of the satellite system.
There is a need for a method and system that is capable of providing a circularly polarized waveform over two bands that are separated by more than 10% of the mid-frequency between the transmit and receive bands.
It is an object of the present invention to generate circularly polarized waves at two frequency bands. It is another object of the present invention to generate circularly polarized waves at two bands separated by more than 10% of the mid-frequency.
A further object of the present invention is to improve isolation between transmit and receive bands over conventional single hybrid-fed elements. It is still a further object of the present invention to excite a patch element using two different hybrids for transmit and receive bands respectively.
The present invention is a dual-band patch antenna element for circular polarization. The patch element is excited by two different hybrids, designed for transmit and receive bands respectively. Each hybrid electromagnetically couples a pair of orthogonal ground plane slots that excite the patch antenna. The hybrid and slot dimensions for the transmit band are different from the hybrid and slot dimensions for the receive band. Isolation can be improved by connecting shunt stubs to the hybrids.
These and other features of the present invention will be better understood with regard to the following description, appended claims, and accompanying drawings.